Spinal muscular atrophy (SMA) type I (Werdnig-Hoffmann disease).

Spinal muscular atrophy type I, also called Werdnig-Hoffmann disease, is the most serious form. The disease appears before the age of 6 months and is characterized by major global hypotonia and abolition of tendon reflexes, with children never being able to sit unaided. Cognitive development is normal and the expressive gaze of these children contrasts with the paralytic attitude. Respiratory involvement predominates in the intercostal muscles, and sometimes brainstem involvement are all serious aspects of the disease. Type I spinal muscular atrophy has been subdivided into 3 groups: - type IA, the clinical signs of which set in between birth and 15 days of life with sudden severe motor impairment, sucking-swallowing disorders attesting to bulbar involvement, respiratory distress. - type IB with onset of symptoms before the age of 3 months, which implies no head control - type IC starting between 3 and 6 months with the possibility of checking head control, often referred to as "I bis" by French practitioners. The development and use of innovative therapies in recent years does actually change the natural course of this disease. But we do not know for sure what the long-term evolution of infants who received these new therapies will be. © 2020 French Society of Pediatrics. Published by Elsevier Masson SAS. All rights reserved.